The present invention relates to ATM (asynchronous transfer mode) edge node switching equipment that provides a function to distribute IP (Internet protocol) data packets to each of destination IP addresses by utilizing an IP-VPN (Internet protocol-virtual private network) function.
1. Description of the Related Art
Recently the Internet has been widely used by utilizing a TCP/IP (transmission control protocol/Internet protocol) in a network of computers. At the Internet, aimed information linked to a WWW (world wide web) can be obtained by using a hyper text through a public network or a leased line.
On the other hand, a LAN (local area network) board being capable of corresponding to an ATM, which is expected to utilize in the future as a back born at the Internet, has begun to be released. The ATM is a data transmission and exchanging technology that is adopted at a next generation public network being a B-ISDN (broad band integrated services digital network). At the ATM, a data packet is called as an ATM cell, and the ATM cell is a 53 byte fixed length packet including a 5 byte header part providing control information for the destination and source address. In this header part, detecting/correcting codes are not included. This ATM cell is transferred from a user terminal to switching equipment, and the switching equipment reads a destination in the header part and transfers the ATM cell to a designated destination user terminal. When the ATM cell is transferred, the ATM cell is stored in the switching equipment temporarily, therefore communication among user terminals whose transmission rates are different is possible. And at the ATM, before starting the communication, the user terminals and switching equipment can secure the transmission bandwidth beforehand. Therefore, it is suitable to transfer streaming data, in which a part of a file being such as audio and video data can be reproduced in the ATM.
And generally, the public network is used at the Internet, but in order to secure the security, by making the public network be a private network like a leased line by utilizing a VPN (virtual private network), a system, in which data transferring through the public network are encrypted, has been gradually used.
Recently a small size business office such as a SOHO (small office home office) has increased, and an instrument, based on an L3-VPN corresponding to the layer 3 of network layers of an OSI (open system interconnection) referring model utilized the Internet, has increased. However, there is a problem that the assurance of quality of service (QOS) such as securing the communication bandwidth in the Internet at the public network can not be achieved.
In order to secure the assurance of the QOS completely, a user must contract with a communication carrier who operates and manages the network for a leased line of the network access layer or an L2-VPN leased line being the layer 2 of physical layer. However, in case of contracting the L2-VPN leased line, when the number of user terminals to be connected to the network increases, the number of the leased lines also increases, and this causes a high cost.
FIG. 1 is a diagram showing a conventional structure of an ATM network used the L2-VPN. As shown in FIG. 1, at a conventional ATM network 10, plural ATM edge node switching equipment 13 is provided, and plural user terminals 11 are connected to each of the plural ATM edge node switching equipment 13 by a mesh connection 12. In this ATM network 10, there is a leased line service transferring an IP data packet, however, the leased line, which connects the plural user terminals 11 and the ATM edge node switching equipment 13, is the L2-VPN system being the mesh connection, consequently, this causes a high cost.